50 
PLANTS OF YELLOWSTONE NATIONAL PARK 
Eriogonum rydbergii is another closely similar species, except 
that it has the leaves densely white-hairy on both sides. 
Eriogonum flavum has yellow flowers and is white-hairy through¬ 
out including the flowers. 
Piper eriogonum ( Eriogonum piperi) is soft-hairy throughout ex¬ 
cept on the lower surface of the leaves. The stems are 4 to 8 inches 
high and the flowers are greenish yellow. 
Cushion eriogonum ( Eriogonum ovalifolium) is low and densely 
soft-hairy. The flowers are yellow or white in a headlike cluster 
at the end of a slender stem which may be 1 to 6 inches long. 
Eriogonum andinum is a small, 
matted, woolly plant with the 
leaves clustered on prostrate 
branches and with short, weak 
stems bearing few flowers which 
are yellow or tinged with purple. 
Eriogonum ochroleucum —-This 
is a low, densely hairy plant, with 
the leaves narrowed into slender 
and often twisted petioles. The 
stems are slender and 4 to 10 
inches high and the flowers are 
creamy white. 
Eriogonum caespitosum is an¬ 
other species that has been re¬ 
ported as occurring in the park. 
Mountain-sorrel (Oxyria digyna) 
is found at high altitudes in wet 
places among rocks. The stout and 
somewhat fleshy stem grows from 
4 to 16 inches high and is smooth. 
The round or kidney-shaped 
leaves are mostly basal and have long petioles. The flowers are 
small and greenish or sometimes reddish. 
Sheep sorrel ( Rumex acetosella) is a European plant which has 
been introduced into this country and has become a rather common 
weed. The leaves have a pleasantly sour taste due to the presence of 
acetic acid. The branching stems are 4 to 12 inches high, and the 
leaves are small, usually less than 2 inches long, the lower ones arrow- 
shaped. The flowers are imperfect, some plants producing stami- 
nate flowers and other plants pistillate. The small, reddish flowers 
are produced in a sort of compound panicle. Rumex paucifolius is 
similar but the leaves are linear to lance-shaped. 
